The present invention relates to a system and method for characterizing a textured surface useful for assessing and/or characterizing textured surfaces of various items, e.g., polishing pads, in particular polishing pads used in chemical-mechanical planarization (CMP), for purposes such as production quality control and development of such items.
CMP polishing is a process currently practiced in the semiconductor and other industries for creating flat surfaces on integrated circuit wafers and magnetic storage disks, among other things. Generally, CMP involves flowing or otherwise placing a polishing slurry or fluid between the wafer, memory disk or other workpiece to be planarized and a CMP polishing pad, and moving the pad and workpiece relative to one another while biasing the pad and workpiece together. CMP polishing pads generally have a textured surface that allows slurry to move throughout the network of voids formed when the peaks and valleys of the textured surface are brought into contact with the surface of the workpiece. The textured surfaces of CMP polishing pads having various topographies adapted to different polishing scenarios are known in the art.
Surface flow resistance is a critical characteristic of CMP polishing pads that impacts flow patterns of the polishing slurry in the voids between the pad and workpiece during polishing. Liquid flow patterns affect the delivery of fresh slurry to the workpiece surface, the removal of polishing debris from the surface and the conveyance of heat from both chemical reaction and mechanical abrasion. More accurate optimization of CMP performance and more effective design of CMP polishing pads and slurries would be possible if the exact flow patterns in the voids could be predicted. However, the surface flow resistance of a CMP polishing pad is impossible to measure dynamically on a CMP machine because the spaces between the pad and workpiece are inaccessible to conventional measuring devices. In addition, CMP generally involves variously overlapping and concurrent physics due to the orbital action of CMP that make it virtually impossible to isolate from CMP data typically collected the effects of fluid flow pattern.
Research and modeling of CMP to date have applied fluid flow treatments adapted from bearing theory, which describes CMP pads in terms of roughness parameters or a distribution of surface peaks, aka “asperities.” These conventional approaches generally suffer from three shortcomings: (1) the pad surface descriptors are not easily related to measurable physical quantities; (2) it is unclear how the pad surface descriptors change under conditions of compression, shear and wetting that prevail in the pad-wafer gap during CMP; and (3) the fluid motion description is oversimplified such that practical features of interest, such as grooves or perforations, are difficult to model.